
;           Copyright Oliver Kowalke 2009.
;  Distributed under the Boost Software License, Version 1.0.
;     (See accompanying file LICENSE_1_0.txt or copy at
;           http://www.boost.org/LICENSE_1_0.txt)

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;  |   0xa8  |   0xac  |   0xb0   |   0xb4  |   0xb8  |   0xbc  |   0xc0  |   0xc4  |
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;  | fc_mxcsr|fc_x87_cw|     <alignment>    |      fbr_strg     |      fc_dealloc   |
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;  |      limit        |       base         |      R12          |        R13        |
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;  |   0xe8  |   0xec  |   0xf0  |   0xf4   |   0xf8  |   0xfc  |  0x100  |  0x104  |
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;  |        R14        |        R15         |       RDI         |       RSI         |
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;  |    66   |   67    |    68    |   69    |    70   |  71     |    72   |    73   |
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;  |        RBX        |         RBP        |        RIP        |       EXIT        |
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; standard C library function
EXTERN  _exit:PROC
.code

; generate function table entry in .pdata and unwind information in
vic_make_context PROC BOOST_CONTEXT_EXPORT FRAME
    ; .xdata for a function's structured exception handling unwind behavior
    .endprolog

    ; first arg of vic_make_context() == top of context-stack
    mov  rax, rcx

    ; reserve 32byte shadow-space for context-function
    sub  rax, 028h

    ; shift address in RAX to lower 16 byte boundary
    ; == pointer to fcontext_t and address of context stack
    and  rax, -16

    ; reserve space for context-data on context-stack
    ; size for fc_mxcsr .. RIP + return-address for context-function
    ; on context-function entry: (RSP -0x8) % 16 == 0
    sub  rax, 0128h

    ; third arg of vic_make_context() == address of context-function
    mov  [rax+0118h], r8

    ; first arg of vic_make_context() == top of context-stack
    ; save top address of context stack as 'base'
    mov  [rax+0d0h], rcx
    ; second arg of vic_make_context() == size of context-stack
    ; negate stack size for LEA instruction (== substraction)
    neg  rdx
    ; compute bottom address of context stack (limit)
    lea  rcx, [rcx+rdx]
    ; save bottom address of context stack as 'limit'
    mov  [rax+0c8h], rcx
    ; save address of context stack limit as 'dealloction stack'
    mov  [rax+0c0h], rcx

    ; save MMX control- and status-word
    stmxcsr  [rax+0a8h]
    ; save x87 control-word
    fnstcw  [rax+0ach]

    ; compute abs address of label finish
    lea  rcx, finish
    ; save address of finish as return-address for context-function
    ; will be entered after context-function returns
    mov  [rax+0120h], rcx

    ; set indicator
    mov  rcx, 1
    mov  [rax], rcx

    ret ; return pointer to context-data

finish:
    ; 32byte shadow-space for _exit() are
    ; already reserved by vic_make_context()
    ; exit code is zero
    xor  rcx, rcx
    ; exit application
    call  _exit
    hlt
vic_make_context ENDP
END
